Magnetic field sensor providing a movement detector

ABSTRACT

A magnetic field sensor has a plurality of magnetic field sensing elements and operates as a motion detector for sensing a rotation or other movement of a target object.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application and claims the benefit ofU.S. patent application Ser. No. 14/529,669, filed on Oct. 31, 2014,which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors, and, moreparticularly, to magnetic field sensors having a substrate with magneticfield sensing elements thereupon to sense a motion of a ferromagneticobject, all arranged in a variety of relative positions.

BACKGROUND

Various types of magnetic field sensing elements are known, includingHall Effect elements and magnetoresistance elements. Magnetic fieldsensors generally include a magnetic field sensing element and otherelectronic components. Some magnetic field sensors also include apermanent magnet (a hard ferromagnetic object) in a so-called “backbiased” arrangement described more fully below. Other magnetic fieldsensors sense motion of a magnet.

Magnetic field sensors provide an electrical signal representative of asensed magnetic field. In some embodiments that have the magnet(back-biased arrangements), the sensed magnetic field is a magneticfield generated by the magnet, in which case, in the presence of amoving ferromagnetic object, the magnetic field generated by the magnetand sensed by the magnetic field sensor varies in accordance with ashape or profile of the moving ferromagnetic object. In contrast,magnetic field sensors that sense a moving magnet directly sensevariations of magnetic field magnitude and direction that result frommovement of the magnet.

Magnetic field sensors (back-biased) are often used to detect movementof features of a ferromagnetic gear, such as gear teeth and/or gearslots or valleys. A magnetic field sensor in this application iscommonly referred to as a “gear tooth” sensor.

In some arrangements, the gear (a target object) is placed upon anotherobject, for example, a camshaft in an engine. Thus, it is the rotationof both the target object (e.g., gear) and the other object (e.g.,camshaft) that is sensed by detection of the moving features of thegear. Gear tooth sensors are used, for example, in automotiveapplications to provide information to an engine control processor forignition timing control, fuel management, anti-lock braking systems,wheel speed sensors, and other operations.

Information provided by the gear tooth sensor to the engine controlprocessor can include, but is not limited to, an absolute angle ofrotation of a target object (e.g., a camshaft) as it rotates, a speed ofthe rotation, and a direction of the rotation. With this information,the engine control processor can adjust the timing of firing of theignition system and the timing of fuel injection by the fuel injectionsystem.

Many types of magnetic field sensors do not provide an accurate outputsignal (e.g., indication of absolute angle, speed, or direction ofrotation) immediately upon power up, upon movement of the target objectfrom zero rotating speed, and/or upon movement slowing to zero rotatingspeed, but instead provide an accurate output signal only once thetarget object has moved through a substantial rotation or is moving withsubstantial speed. For example, in one type of magnetic field sensordescribed in U.S. Pat. No. 6,525,531, entitled “Detection of PassingMagnetic Articles while Adapting the Detection Threshold,” issued Feb.25, 2003, a positive digital-to-analog converter (PDAC) and a negativedigital-to-analog converter (NDAC) track positive and negative peaks ofa magnetic field signal, respectively, for use in generating a thresholdsignal. A varying magnetic field signal is compared to the thresholdsignal. However, the outputs of the PDAC and the NDAC may not beaccurate indications of the positive and negative peaks of the magneticfield signal until several cycles of the signal (i.e., signal peaks)occur (i.e., until several gear teeth have passed). This type ofmagnetic field sensor, which generally requires time to become fullyaccurate, is referred to herein as a so-called “precision rotationdetector.”

In contrast, a “true power on state” (TPOS) detector can provide anaccurate output signal shortly after movement of a target object (e.g.,camshaft) from zero rotating speed, or a low rotation speed in someapplications of, for example, less than 100 rpm, or also shortly beforemovement slowing to zero rotating speed. Furthermore, even when thetarget object is not moving, the TPOS detector can provide an indicationof whether the TPOS detector is in front of a tooth or a valley of agear. However, when the target object is stationary, the conventionalTPOS detector is not able to identify an absolute or relative angle ofrotation of the target object. The TPOS detector can be used inconjunction with a precision rotation detector within a commonintegrated circuit, each providing information to the engine controlprocessor at different times. For simplicity, TPOS detectors andprecision rotation detectors are shown herein within a common integratedcircuit. However, the TPOS detector or the precision rotation detectorcan also be used alone in separate circuits.

As described above, the conventional TPOS detector provides an accurateoutput signal with only a small initial rotation of the target object,and before the precision rotation detector can provide an accurateoutput signal. The TPOS detector can provide information to the enginecontrol processor that can be more accurate than information provided bythe precision rotation detector for time periods at the beginning and atthe end of rotation of the target object (e.g., start and stop of theengine and camshaft), but which may be less accurate when the object isrotating at speed. For magnetic field sensor arrangements that have botha TPOS detector and a precision rotation detector within a commonintegrated circuit, when the object is not rotating or rotating slowly,the engine control processor can use the TPOS detector. When rotating atspeed, the engine control processor can primarily use rotationinformation provided by the precision rotation detector. In mostconventional applications, once the magnetic field sensor switches touse the precision rotation detector, it does not return to use the TPOSdetector until the target object stops rotating or nearly stopsrotating.

A conventional TPOS detector is described in U.S. Pat. No. 7,362,094,entitled “Method and Apparatus for Magnetic Article Detection,” issuedApr. 22, 2008. The conventional TPOS detector includes a comparator forcomparing the magnetic field signal to a fixed, often trimmed, thresholdsignal. The conventional TPOS detector can be used in conjunction withand can detect rotational information about a TPOS cam (like a gear),which is disposed upon a target object, e.g., an engine camshaft,configured to rotate.

An example of an output signal from a conventional TPOS detector has atleast two states, and typically a high and a low state. The state of theconventional TPOS output signal is high at some times and low at othertimes as the target object rotates, in accordance with features on theTPOS cam (or gear) attached to the target object.

Similarly, an output signal from a conventional precision rotationdetector also has at least two states, and typically a high and a lowstate. The state of the conventional precision rotation detector outputsignal is high at some times and low at other times as the target objectrotates, also in accordance with features on the TPOS cam (or gear)attached to the target object

As described above, conventional TPOS detectors have the ability todifferentiate a gear tooth from a gear valley (i.e., gear “features”),and to make such detection when the gear is rotating and when the gearis not rotating. In contrast, some conventional precision rotationdetectors have the ability to differentiate a gear tooth from a gearvalley when the gear is rotating, but not when the gear is stationary.Detectors that can identify a gear tooth from a valley are sometimesreferred to as “tooth detectors.” Thus, TPOS detectors are usually toothdetectors. Some precision rotation detectors can also be toothdetectors.

While detection of gear teeth can be used by some magnetic fieldsensors, other magnetic field sensors can sense passing magnetic polesof a ring magnet (i.e., features). Thus, as used herein, the term“feature detector” is used to describe either a tooth detector or adetector of magnetic poles.

Some other conventional precision rotation detectors are unable todifferentiate a gear tooth from a valley (or a north pole from a southpole of a ring magnet), but instead, can differentiate an edge of atooth of the gear from the tooth or the valley. Such detectors aresometimes referred to as “edge detectors.” Usually, TPOS detectors arenot edge detectors. However, some precision rotation detectors can beedge detectors.

The conventional magnetic field sensor must achieve an accurate outputsignal that accurately differentiates between gear teeth and gearvalleys even in the presence of an air gap between the magnetic fieldsensor and the gear that may change from installation to installation orfrom time to time. Still further, the conventional magnetic field sensormust achieve these differentiations even in the presence of unit-to-unitvariations in relative positions of the magnet and the magnetic fieldsensing element within the magnetic field sensor. Still further, theconventional magnetic field sensor must achieve these differentiationseven in the presence of unit-to-unit variations in the magnetic fieldgenerated by the magnet. Still further, the conventional magnetic fieldsensor must achieve these differentiations even in the presence ofvariations of an axial rotation of the magnetic field sensor relative tothe gear. Still further, the conventional magnetic field sensor mustachieve these differentiations even in the presence of variations oftemperature around the magnetic field sensor.

The above effects result in expensive design choices. In particular,some of the above effects result it use of an expensive magnet describedbelow in conjunction with FIG. 1.

It would be desirable to provide a magnetic field sensor that canachieve an accurate output signal that accurately differentiates betweengear teeth and gear valleys while using a simpler and less expensivemagnet.

SUMMARY

A magnetic field sensor achieves an accurate output signal thataccurately differentiates between gear teeth and gear valleys whileusing a simpler and less expensive magnet. The differentiation isachieved even in the presence of variations of mechanical and thermalparameters associated with the magnetic field sensor.

In accordance with an example useful for understanding an aspect of thepresent invention, a magnetic field sensor for measuring movement of atarget object, the movement in an x-z plane within x-y-z Cartesiancoordinates with x, y, and z orthogonal axes, a tangent to a directionof movement of a surface of the target object proximate to the magneticfield sensor substantially parallel to the x axis, includes a substratehaving a major planar surface within about twenty degrees of parallel tothe x-z plane. The magnetic field sensor also includes a plurality ofmagnetic field sensing elements disposed upon the major planar surfaceof the substrate. Each one of the plurality of magnetic field sensingelements has a major response axis substantially parallel to the majorplanar surface of the substrate. The plurality of magnetic field sensingelements is configured to generate a respective plurality of magneticfield signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a block diagram of a prior art magnetic field sensor having amagnetic field sensing element, an electronic circuit, and a magnet;

FIG. 1A is a block diagram of an example of an electronic circuit thatcan be used as the electronic circuit of FIG. 1;

FIG. 2 is a block diagram of another prior art magnetic field sensorhaving three magnetic field sensing elements, an electronic circuit, anda magnet;

FIG. 2A is a block diagram of an example of an electronic circuit thatcan be used as the electronic circuit of FIG. 2;

FIG. 3 is a block diagram showing an example of a magnetic field sensorhaving two magnetic field sensing elements and an electronic circuitboth disposed on a substrate, and also having a magnet;

FIG. 4 is a block diagram showing an example of another magnetic fieldsensor having two magnetic field sensing elements and an electroniccircuit both disposed on a substrate, and having a magnet different thanthe magnet of FIG. 3;

FIG. 5 is a block diagram showing an example of the two magnetic fieldsensing elements and an example of the electronic circuit of FIGS. 3 and4;

FIG. 6 is a block diagram showing an example of a magnetic field sensorhaving a plurality of magnetic field sensing elements and an electroniccircuit both disposed on a substrate, and also having a magnet;

FIG. 7 is a block diagram showing an example of another magnetic fieldsensor having a plurality of magnetic field sensing elements and anelectronic circuit both disposed on a substrate, and having a magnetdifferent than the magnet of FIG. 3;

FIG. 8 is a block diagram showing an example of the plurality ofmagnetic field sensing elements and an example of the electronic circuitof FIGS. 6 and 7;

FIG. 9 is a block diagram showing another example of the plurality ofmagnetic field sensing elements and another example of the electroniccircuit of FIGS. 6 and 7;

FIG. 10 is a block diagram showing an example of a magnetic field sensorhaving a circular vertical Hall (CVH) sensing element and an electroniccircuit both disposed on a substrate, and also having a magnet;

FIG. 11 is a block diagram showing an alternate example of the twomagnetic field sensing elements as compared to FIG. 5 and can be usedwith the electronic circuit of FIG. 5;

FIG. 12 is a block diagram showing an alternate arrangement of any ofthe above magnetic field sensors but for which magnetic field sensingelements contained therein overlap a sensed ferromagnetic object;

FIG. 13 is a block diagram showing an alternate arrangement of themagnetic field sensors represented in FIG. 12;

FIG. 14 is a block diagram showing an alternate arrangement of any ofthe above magnetic field sensors but for which a sensed ferromagneticobject is a ring magnet;

FIG. 15 is a block diagram showing an alternate arrangement of themagnetic field sensors represented in FIG. 14, but for which magneticfield sensing elements contained therein overlap the ring magnet; and

FIG. 16 is a block diagram showing an alternate arrangement of magneticfield sensing elements arranged in an arc as compared to magnetic fieldsensing elements arranged in a line shown in FIGS. 6 and 7.

DETAILED DESCRIPTION

Before describing the present invention, some introductory concepts andterminology are explained.

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, MTJ, AMR)and vertical Hall elements tend to have axes of sensitivity parallel toa substrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

As used herein, the term “accuracy,” when referring to a magnetic fieldsensor, is used to refer to a variety of aspects of the magnetic fieldsensor. These aspects include, but are not limited to, an ability of themagnetic field sensor to differentiate: a gear tooth from a gear valley(or, more generally, the presence of a ferromagnetic object from theabsence of a ferromagnetic object) when the gear is not rotating and/orwhen the gear is rotating (or, more generally, when a ferromagneticobject is moving or not moving), an ability to differentiate an edge ofa tooth of the gear from the tooth or the valley of the gear (or, moregenerally, the edge of a ferromagnetic object or a change inmagnetization direction of a hard ferromagnetic object), and arotational accuracy with which the edge of the gear tooth is identified(or, more generally, the positional accuracy with which an edge of aferromagnetic object or hard ferromagnetic object can be identified).Ultimately, accuracy refers to output signal edge placement accuracy andconsistency with respect to gear tooth edges passing by the magneticfield sensor.

The terms “parallel” and“perpendicular” are used in various contextsherein. It should be understood that the terms parallel andperpendicular do not require exact perpendicularity or exactparallelism, but instead it is intended that normal manufacturingtolerances apply, which tolerances depend upon the context in which theterms are used. In some instances, the term “substantially” is used tomodify the terms “parallel” or “perpendicular.” In general, use of theterm “substantially” reflects angles that are beyond manufacturingtolerances, for example, within +/−ten degrees.

It is desirable for magnetic field sensors to achieve a certain level oramount of accuracy even in the presence of variations in an air gapbetween the magnetic field sensor and the gear that may change frominstallation to installation or from time to time. It is also desirablefor magnetic field sensors to achieve accuracy even in the presence ofvariations in relative positions of the magnet and the magnetic fieldsensing element within the magnetic field sensor. It is also desirablefor magnetic field sensors to achieve accuracy even in the presence ofunit-to-unit variations in the magnetic field generated by a magnetwithin the magnetic field sensors. It is also desirable for magneticfield sensors to achieve accuracy even in the presence of variations ofan axial rotation of the magnetic field sensors relative to the gear. Itis also desirable for magnetic field sensors to achieve accuracy even inthe presence of temperature variations of the magnetic field sensors.

Examples below describe a particular gear (or a particular ring magnet)as may be used upon an engine camshaft target object. However, similarcircuits and techniques can be used with other cams or gears or ringmagnet disposed upon the engine camshaft, or upon other rotating partsof an engine, vehicle, or a machine (e.g., crank shaft, transmissiongear, anti-lock braking system (ABS)), or upon rotating parts of adevice that is not an engine. Other applications may include lineartranslation sensors or other sensors where the sensed object is not arotating gear or ring magnet, but is a linear arrangement.

The gear (or target) or the ring magnet is not a part of the magneticfield sensors described below. The gear can have ferromagnetic gearteeth, which are generally soft ferromagnetic objects, but which canalso be hard ferromagnetic objects, patterns, or domains which may ormay not have actual physical changes in their shape.

Examples are shown below of magnetic field sensors that can senseferromagnetic gear teeth having gear teeth edges upon a gear configuredto rotate. Other examples are shown below of magnetic field sensors thatcan sense north and south poles having pole edges upon a ring magnetconfigured to rotate. However, the magnetic field sensors can be used inother applications. The other applications include, but are not limitedto, sensing ferromagnetic objects or poles upon a structure configuredto move linearly.

As used herein, the term “features” is used to describe gear teeth orgear valleys upon a gear and also to describe north or south poles upona ring magnet.

As used herein, the term “baseline” and the phrase “baseline level” areused to describe a lowest magnitude (which may be near zero or may besome other magnetic field) of a magnetic field experienced by a magneticfield sensing element within a magnetic field sensor when the magneticfield sensor is operating in a system. In some systems, this lowestmagnetic field occurs when a magnetic field sensor is proximate to agear valley as opposed to a gear tooth.

It will be understood that, in general, a difference between thebaseline level and a higher level achieved, for example, when a geartooth is proximate to a magnetic field sensor, is related to an abilityof the magnetic field sensor to differentiate between a gear tooth and avalley, and thus, related to accuracy of the magnetic field sensor.

While it is described above that a baseline level is generated when amagnetic field sensor is proximate to a gear valley and a higher levelis achieved when the magnetic field sensor is proximate to a gear tooth,other physical arrangements are also possible, for example, a reversearrangement for which a baseline level is generated when a magneticfield sensor is proximate to a gear tooth and a higher level is achievedwhen the magnetic field sensor is proximate to a gear valley.

As used herein, the term “processor” is used to describe an electroniccircuit that performs a function, an operation, or a sequence ofoperations. The function, operation, or sequence of operations can behard coded into the electronic circuit or soft coded by way ofinstructions held in a memory device. A “processor” can perform thefunction, operation, or sequence of operations using digital values orusing analog signals.

In some embodiments, the “processor” can be embodied in an applicationspecific integrated circuit (ASIC), which can be an analog ASIC or adigital ASIC. In some embodiments, the “processor” can be embodied in amicroprocessor with associated program memory. In some embodiments, the“processor” can be embodied in a discrete electronic circuit, which canbe an analog or digital.

As used herein, the term “module” is used to describe a “processor.”

A processor can contain internal processors or internal modules thatperform portions of the function, operation, or sequence of operationsof the processor. Similarly, a module can contain internal processors orinternal modules that perform portions of the function, operation, orsequence of operations of the module.

It should be understood that electronic functions that may be describedbelow to be analog functions can instead be implemented in digitalcircuits, in processors, or in modules. For example, it will berecognized that a comparator can be implemented as an analog comparatorthat compares analog voltages, as a digital comparator that comparesdigital values, or as a processor or module that compares digitalvalues. Examples shown herein to be analog examples do not limit thescope of described embodiments to be analog embodiments only.

As used herein, the term “predetermined,” when referring to a value orsignal, is used to refer to a value or signal that is set, or fixed, inthe factory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

As used herein, the term “active electronic component” is used todescribe and electronic component that has at least one p-n junction. Atransistor, a diode, and a logic gate are examples of active electroniccomponents. In contrast, as used herein, the term “passive electroniccomponent” as used to describe an electronic component that does nothave at least one p-n junction. A capacitor and a resistor are examplesof passive electronic components.

As used herein, the term “target object” is used to refer to aferromagnetic gear, a ferromagnetic ring magnet, a non-ferromagneticconductive object, or another type of target object, position ormovement of which is detected by magnetic field sensor describe herein.In some embodiments, the target object can be coupled to another object,for example, a camshaft of an engine. Thus, the detected position ormovement of the target object can be used to identify a position ormovement of the other object.

Referring to FIG. 1, an example of a magnetic field sensor 10 isresponsive to a gear 22 having ferromagnetic gear teeth, e.g., gearteeth 22 a, 22 b, 22 c. It should be recognized that the gear 22 is butone type of “ferromagnetic target object,” or simply “target object,”which the magnetic field sensor 10 can be responsive. In other magneticsystems, the ferromagnetic target object may include a permanent magnet(or a hard ferromagnetic material), for example, the above-describedring magnet having alternating north and south poles. Ring magnets areshown and described below in conjunction with FIGS. 14-16.

The magnetic field sensor 10 includes a magnetic field sensing element12 coupled to an electronic circuit 16. The magnetic field sensingelement 12 and the electronic circuit 16 can be disposed upon (i.e.,integrated within or upon) a substrate 14. For clarity, here themagnetic field sensing element 12 is shown to be a Hall element with anexaggerated size, and rotated out of the plane of the substrate 14.Furthermore, for clarity, the Hall element 12 is shown to be on top ofthe substrate 14, but it will be appreciated that Hall elements areusually disposed upon or within a surface of a substrate of anintegrated circuit.

The magnetic field sensor 10 can also include a magnet 18 (e.g. apermanent magnet or hard ferromagnetic material). The magnet 18 isconfigured to generate a magnetic field, which is generally directedalong an axis 24 at the position of the magnetic field sensing element12, and which is subject to direction and amplitude changes dependingupon positions of the gear teeth 22 a, 22 b, 22 c relative to themagnetic field sensor 10. However, the structure of the magnetic fieldat faces of the magnet 18 can be more complex due to a core 20.

The electronic circuit 16 is configured to generate an output signal(not shown). The output signal, when the gear is not moving, isindicative of whether the magnetic field sensor 10 is over a gear toothor a gear valley. Thus, the magnetic field sensor 10 is sometimesreferred to as a “tooth detector” (or feature detector) as opposed to an“edge detector.” The output signal, when the gear is rotating, has anedge rate or a frequency indicative of a speed of rotation of the gear.Edges or transitions of states of the output signal can be used toidentify positions of edges of the gear teeth as they pass by themagnetic field sensor.

The magnet 18 can include the central core 20 comprised of a softferromagnetic material disposed within the magnet 18. An example of amagnet with a core is described in U.S. Pat. No. 6,278,269, entitled“Magnet Structure,” issued Aug. 21, 2001, which patent is assigned tothe assignee of the present invention and incorporated herein byreference in its entirety. As described in U.S. Pat. No. 6,278,269, thepole configuration provided by the magnet 18 with the core 20 lowers thebase field (or baseline) of a flux density of the magnetic field at somepoints above the surface of the core 20 (e.g., to the left of the coreas shown) when a valley of the gear 22 is proximate to the magneticfield sensor 10. A predetermined baseline (e.g., within a range of about+/six hundred Gauss) at the magnetic field sensing element 12, and aresulting differential magnetic field signal 12 a, 12 b (i.e., an analogdifferential proximity signal) near zero, can be achieved with properdesign.

In contrast, when a gear tooth of the gear 22 is proximate to themagnetic field sensing element 12, the magnetic field sensing element 12experiences a higher magnetic field and generates the differentialmagnetic field signal 12 a, 12 b with a higher value. As describedabove, a difference between the baseline magnetic field and the highermagnetic field is related to ultimate accuracy of the magnetic fieldsensor 10.

The baseline magnetic field, which can occur when the magnetic fieldsensor 10 is proximate to a valley in the gear 22, remains relativelylow, with little change, even as the air gap between the gear 22 and themagnetic field sensor 10 varies. This advantageous result of lowbaseline substantially independent of air gap is achieved by operationof the core 20, which results in opposite magnetic poles being presentedat the face of the core 20 (i.e., left side as shown) proximate to themagnetic field sensing element 12, particularly when the magnetic fieldsensing element 12 is proximate to a valley in the gear 22. This effectis also described in U.S. Pat. No. 5,781,005, issued Jul. 14, 1998,entitled “Hall-Effect Ferromagnetic-Article-Proximity Sensor,” whichpatent is assigned to the assignee of the present invention andincorporated herein by reference in its entirety.

The above-described low baseline, which occurs when the magnetic fieldsensor is proximate to a gear valley, results in an enhanced ability ofthe electronic circuit 16 to differentiate the presence of the geartooth from a gear valley.

The above-described low baseline also provides an ability to more easilycompensate for temperature effects, since the baseline magnetic field isrelatively small, and therefore, circuit variations that occur due totemperature can have less influence when the magnetic field sensor 10 isproximate to a valley in the gear 22. Essentially, any error in thecircuitry is able to be well corrected near the baseline magnetic fieldlevel or range, since any multiplication of the error (near zero) issmaller. Therefore, a magnetic field threshold used to distinguish atooth from a valley can be made smaller while maintaining precisionbecause there is less noise or error in the system over its operatingconditions such as temperature, or humidity.

The magnetic field described above and provided by the magnet 18 withthe core 20 results in an improved accuracy of the magnetic field sensor10. For example, the low baseline allows the magnetic field sensingelement 12 to be somewhat statically misaligned from a center of themagnet 18, as will occur due to unit-to-unit variations of mechanicalalignments, without sacrificing accuracy of the magnetic field sensor10. Accuracy is discussed above.

Referring now to FIG. 1A, an example of a prior art electronic circuit50 can be the same as or similar to electronic circuit 16 of FIG. 1. Theelectronic circuit 50 can include in amplifier 54 coupled to receive adifferential signal 52 a, 52 b, which can be the same as or similar tothe differential signal 12 a, 12 b generated by the magnetic fieldsensing element 12 of FIG. 1. The amplifier 54 is configured to generatean amplified signal 54 a, which, in some embodiments, can split into twochannels, a TPOS detector channel and a precision rotation detectorchannel.

In the true power on state (TPOS) channel, a TPOS detector 56 can becoupled to receive the amplified signal 54 a and configured to generatea TPOS output signal 56 a. In some embodiments, the TPOS detector 56 caninclude a comparator (not shown) configured to compare the amplifiedsignal 54 a with a fixed (and trimmed) threshold. In these embodiments,the TPOS output signal 56 a can be a two-state binary signal for which ahigh state is indicative of a gear tooth being proximate to the magneticfield sensor 10 of FIG. 1 and a low state is indicative of a gear valleybeing proximate to the magnetic field sensor 10, or vice versa.

In the precision rotation detector channel, an automatic gain control(AGC) 58 can be coupled to receive the amplified signal 54 a andconfigured to generate a gain controlled signal 58 a. A precisionrotation detector 60 can be coupled to receive the gain controlledsignal 58 a and configured to generate a precision rotation detectoroutput signal 60 a. Like the TPOS output signal 56 a, the precisionrotation detector output signal 60 a can be a two-state binary signalfor which a high state is indicative of a gear tooth being proximate tothe magnetic field sensor 10 of FIG. 1 and a low state is indicative ofa gear valley being proximate to the magnetic field sensor 10, or viceversa. Thus, both the TPOS detector 56 and the precision rotationdetector 60 can be “tooth detectors” (i.e., “feature detectors”).However, it should be understood that the precision rotation detectorchannel uses the AGC 58, which, when the gear 22 is not rotating, willsettle to an undesirable gain, resulting, once the gear 22 starts torotate, in a period of time during which the gain is incorrect and theprecision rotation detector is not fully accurate. Even if the AGC 58were not used, still the precision rotation detector 60 uses internalthresholds that are properly updated only when the gear 22 is rotating.However, in other embodiments, the threshold can be supplied fromoutside of the electronic circuit 50.

In some embodiments, the thresholds for the TPOS detector 56 and/or forthe precision rotation detector 60 are stored and later recalled andused. Storage of thresholds is described below in conjunction with FIG.9. The same storage techniques can be used in conjunction with all ofthe magnetic field sensors described herein.

In some alternate embodiments, the precision rotation detector 60 can bean “edge detector,” which is unable to identify whether the magneticfield sensor 12 is proximate to a gear tooth or a gear valley,particularly when the gear is not moving, but which is able to senseedges of gear teeth as they move past the magnetic field sensor 10.

Precision rotation detectors, e.g., the precision rotation detector 60,can have a variety of configurations. Some configurations are describedin the above mentioned U.S. Pat. No. 6,525,531. However, other forms ofprecision rotation detectors are also known, including some that havetwo or more magnetic field sensing elements.

In general, from discussion above, it will be appreciated that the TPOSoutput signal 56 a is indicative of whether the magnetic field sensingelement 12 is proximate to a gear tooth or a gear valley, even when thegear, e.g., the gear 22 of FIG. 1, is stationary. However, since theTPOS detector 56 uses a fixed threshold, in some embodiments, havinglimited adjustment at power up, variations in the edge placement in theTPOS output signal 56 a will occur due to a variety of factors,including, but not limited to, temperature variations, and variations inthe air gap between the magnetic field sensing element 12 and the gear22.

Unlike the TPOS detector 56, which uses fixed thresholds, the precisionrotation detector 60 continually makes adjustments of thresholds toprovide the precision rotation detector output signal 60 a with betteraccuracy of edge placements of the precision rotation detector outputsignal 60 a relative to physical positions of gear teeth. As describedabove, in part, it is these adjustments that make the precision rotationdetector less accurate when it is first powered up or when the gear 22first starts to rotate.

In some embodiments for which the TPOS detector 56 and the precisionrotation detector 60 are integrated onto a common substrate, amultiplexer/output module 62 can be coupled to receive the TPOS outputsignal 56 a and coupled to receive the precision rotation detectoroutput signal 60 a. Select logic 64 can provide a selection signal 64 a,received by the multiplexer/output module 62. Depending upon the stateof the selection signal 64 a, the multiplexer/output module 62 isconfigured to generate an output signal 62 a representative of aselected one of the TPOS output signal 56 a or the precision rotationdetector output signal 60 a. The output signal 62 a can be provided in avariety of signal formats, including, but not limited to, a SENT format,an I²C format, a PWM format, or a two-state format native to the TPOSoutput signal 56 a and to the precision rotation detector output signal60 a.

In some examples, the select logic 64 selects the output signal 62 a tobe representative of the TPOS output signal 56 a for a predeterminedamount of time after the gear 22 starts rotating as indicated by theTPOS output signal 56 a. Thereafter, the select logic 64 selects theoutput signal 62 a to be representative of the precision rotationdetector output signal 60 a.

Referring now to FIG. 2, another example of a prior art magnetic fieldsensor 200 is responsive to a gear 214 having gear teeth, e.g., gearteeth 214 a, 214 b, 214 c. The magnetic field sensor 200 includes threemagnetic field sensing elements 202, 204, 206 coupled to an electroniccircuit 210. In some embodiments, the magnetic field sensing elements202, 204 are separated in a direction perpendicular to an axis 216 by adistance between about 1.5 millimeters and about 3.0 millimeters, andthe magnetic field sensing element 206 is located midway between themagnetic field sensing elements 202, 204.

The three magnetic field sensing elements 202, 204, 206 and anelectronic circuit 210 can be disposed upon (i.e., integrated within orupon) a substrate 208. For clarity, here the magnetic field sensingelements 202, 204, 206 are shown to be Hall elements with an exaggeratedsize, and rotated out of the plane of the substrate 208. Furthermore,for clarity, the Hall elements 202, 204, 206 are shown to be on top ofthe substrate 208, but it will be appreciated that Hall elements areusually disposed upon or within a surface of a substrate of anintegrated circuit.

The magnetic field sensor 200 can also include a magnet 212. The magnet212 is configured to generate a magnetic field, which is generallydirected along an axis 216 at the position of the magnetic field sensingelements 202, 204, 206.

The electronic circuit 210 is configured to generate an output signal(not shown). An exemplary electronic circuit 210 is described below inconjunction with FIG. 2A. Let it suffice here to say that the electroniccircuit generates differences of signals. Thus, it will be apparent thatthe magnetic field sensor 200 is an edge detector and not a toothdetector.

The output signal, when the gear 214 is rotating, is indicative speed ofrotation of the gear 214 and also indicative of positions of edges ofthe gear teeth. The magnetic field sensor 200 is unable to provide aTPOS function, and, when the gear 214 is stationary, is unable toidentify whether the magnetic field sensing elements 202, 204, 206 areproximate to a gear tooth or a valley in the gear 214.

The magnet 212 can be comprised of one uniform material, and can have nocentral core, which is shown and described in conjunction with FIG. 1.However, in other embodiments, the magnet 212 can have a central corethe same as or similar to that shown and described in conjunction withFIG. 1. In still other embodiments, the magnet 212 can have a corecomprised of air or a core comprised of a non-ferromagnetic material.

The magnetic field sensor 200 uses the three magnetic field sensingelements 202, 204, 206 to generate a respective three differentialsignals 202 a, 202 b, and 204 a, 204 b, and 206 a, 206 b. Though thesimple magnet 212 does not provide the low baseline of a magnet with acore, differences of the above differential signals result in the effectof a low baseline. In essence, when the three magnetic field sensingelements 202, 204, 206 experience the same magnetic field, adifferencing of the above differential signals results in a zeroelectronic signal.

Referring now to FIG. 2A, an example of a prior art electronic circuit250 can be the same as or similar to electronic circuit 210 of FIG. 2.The electronic circuit 250 can include amplifiers 258, 260, 262 coupledto receive differential signals 252 a, 252 b, and 254 a, 254 b, and 256a, 256 b, respectively. The differential signal 252 a, 252 b can be thesame as or similar to the differential signal 202 a, 202 b, thedifferential signal 254 a, 254 b can be the same as or similar to thedifferential signals 204 a, 204 b, and the differential signal 256 a,256 b can be the same as or similar to the differential signal 206 a,206 b generated, respectively, by the magnetic field sensing elements202, 204, 206 of FIG. 2. The amplifiers 258, 260, 262 are configured togenerate amplified signals 258 a, 260 a, 262 a, respectively.

The amplified signals 258 a, 260 a are received by a first differencingmodule 264, which is configured to generate a first difference signal264 a. The amplified signals 260 a, 262 a are received by a seconddifferencing module 266, which is configured to generate a seconddifference signal 266 a.

The electronic circuit 250 includes two precision rotation detectorchannels, described above in conjunction with FIG. 1A. A AGCs 270, 276can be the same as or similar to the AGC 56 of FIG. 1A. Precisionsrotation detectors 272, 278 can be the same as or similar to theprecision rotation detector 60 of FIG. 1A. The precision rotationdetector 272 can generate a precision rotation detector output signal272 a and the precision rotation detector 278 can generate a precisionrotation detector output signal 278 a. The precision rotation detectoroutput signals 272 a, 278 a can be the same as or similar to theprecision rotation detector output signal 60 a of FIG. 1A.

A speed and direction module 274 can be coupled to receive the precisionrotation detector output signals 272 a, 278 a.

It should be apparent that the precision rotation detector outputsignals 272 a, 278 a are at relative phases that are determined by adirection of rotation of the gear 214. It should also be apparent thatthe state transition rates of the precision rotation detector outputsignals 272 a, 278 a are representative of a speed of rotation of thegear 214.

The speed and direction module is configured to generate an outputsignal that can be representative of at least one of the speed ofrotation or a direction of rotation of the gear 214. In someembodiments, the output signal 62 a is representative of both the speedof rotation and the direction of rotation.

Referring now to FIG. 3, a magnetic field sensor 300 is responsive to agear 322 having gear teeth, e.g., gear teeth 322 a, 322 b, 322 c. Themagnetic field sensor 300 can include two magnetic field sensingelements 304, 306 coupled to an electronic circuit 314. In someembodiments, the magnetic field sensing elements 304, 306 are separatedin a direction along an axis 308 between the two magnetic field sensingelements 304, 306 by a distance between about 0.2 millimeters and about3.0 millimeters.

In some embodiments, the two magnetoresistance elements 304, 306 have aseparation between about one half and about one and one half of a widthof a ferromagnetic target object feature, for example, a gear tooth of aferromagnetic gear 322 or a magnetic domain of a ferromagnetic ringmagnet. In some other embodiments, the two magnetoresistance elements304, 306 have a separation between about one half and about twice thewidth of the ferromagnetic target object feature. However, in otherembodiments, the separation is much smaller than half of the width, forexample, one one hundredth of the width, or larger than twice the width.

The two magnetic field sensing elements 304, 306 and the electroniccircuit 314 can be disposed upon a major surface 302 a of (i.e.,integrated within or upon) a substrate 302. For clarity, here themagnetic field sensing elements 304, 306 are shown to bemagnetoresistance elements. In other embodiments, the magnetic fieldsensing elements 304, 306 are Hall effect elements, e.g., vertical Halleffect elements.

The magnetic field sensor 300 can also include a magnet 332. The magnet332 is configured to generate a magnetic field, which is generallydirected along an axis 308 at the position of the magnetic field sensingelements 304, 306, and is generally parallel to the major surface 302 aof the substrate 302.

The two magnetic field sensing elements 304, 306 have respective maximumresponse axes parallel to the major surface 302 of the substrate 302. Insome embodiments, the maximum response axes are parallel to each other.In some embodiments, the maximum response axes are substantiallyparallel to the axis 308. In other embodiments, the maximum responseaxes are substantially perpendicular to the axis 308.

A line perpendicular to the major surface 302 a of the substrate (i.e.,into the page) and intersecting the substrate 302, also intersect themagnet 332 and does not intersect the gear 322. Furthermore, in someembodiments, the two magnetic field sensing elements 304, 306 aredisposed at positions such that an axis (e.g., 308) between (i.e.,passing through) the two magnetic field sensing elements 304, 306 doesnot intersect the gear 322. In some embodiments, the axis (e.g., 308)between (i.e., passing through) the two magnetic field sensing elements304, 306 is substantially parallel to a tangent 330 to a direction ofmovement, e.g., 326, of the gear 322.

In the embodiment shown, a line between north (N) and south (S) poles ofthe magnet 332 is substantially parallel to the major surface 302 a ofthe substrate 302, and is substantially parallel to the axis (e.g., 308)between (i.e., passing through) the two magnetic field sensing elements304, 306. In some embodiments, the line between the north and southpoles of the magnet 332 does not intersect the gear 322 and is not in adirection toward the gear 322.

The electronic circuit 314 is configured to generate an output signal(not shown). An exemplary electronic circuit 314 is described below inconjunction with FIG. 5. Let it suffice here to say that the electroniccircuit 314 can generate a difference of signals in accordance with anelectronic circuit described below in conjunction with FIG. 5. Thus, itwill be apparent that the magnetic field sensor 300 can be an edgedetector. However, using other electronic circuits, the other electroniccircuit can generate a sum of signals, in which case, the magnetic fieldsensor 300 can be a tooth detector (i.e., a feature detector).

For an edge detector, the output signal, when the gear 322 is rotating,is indicative of speed of rotation of the gear 322 and also indicativeof positions of edges of the gear teeth. For a tooth detector, theoutput signal, when the gear 322 is rotating, is indicative of speed ofrotation of the gear 322 and also indicative of positions near tocenters of the gear teeth or gear valleys.

While the gear 322 is shown, in other embodiments described below inconjunction with FIGS. 14 and 15, the gear 322 (and also gears describedin other figures below) can be replaced by a ring magnet.

The magnet 332 can be comprised of one uniform material, and can have nocentral core, which is shown and described in conjunction with FIG. 1.However, in other embodiments, the magnet 332 can have a central corethe same as or similar to that shown and described in conjunction withFIG. 1. In still other embodiments, the magnet 332 can have a corecomprised of air or a core comprised of a non-ferromagnetic material.The core can have an axis aligned with an axis 308.

The magnetic field sensor 300 uses the two magnetic field sensingelements 304, 306 to generate a respective two magnetic field signals.Though the simple magnet 332 does not provide the low baseline of amagnet with a core, differences of the above two magnetic field signalsresult in an effect similar to a low baseline. In essence, when the twomagnetic field sensing elements 304, 306 experience the same magneticfield (i.e., proximate to a gear tooth or a gear valley), a differencingof the above differential signals results in a zero electronic signal.

The magnetic field sensor 300 can be rotated in a direction 316 to anext position one hundred eighty degrees apart from the position shown,with no degradation of performance. However, intermediate rotations mayresult in a degradation of performance.

The magnetic field sensor 600 can be rotated in a direction of and arrow318 with a center of rotation anywhere along a line 324, throughapproximately +/−twenty degrees, without substantial degradation ofperformance.

In some embodiments, the magnetic field sensing elements, 304, 306, aremagnetoresistance elements. In other embodiments, the magnetic fieldsensing elements are Hall effect elements, e.g., vertical Hall effectelements. However, it is advantageous to use magnetic field sensingelements for which respective axes of maximum sensitivity are parallelto the axis 308.

Referring now to FIG. 4, in which like elements of FIG. 3 are shownhaving like reference designations, a magnetic field sensor 400 is likethe magnetic field sensor 300 of FIG. 3. However, the magnetic fieldsensor 400 has a different magnet 402 for which a line between north (N)and south (S) poles of the magnet 402 is substantially parallel to themajor surface 302 a of the substrate 302, but substantiallyperpendicular to the axis (e.g., 308) between (i.e., passing through)the two magnetic field sensing elements 304, 306. In some embodiments,the line between the north and south poles of the magnet 402 is in adirection toward the gear 322.

In some embodiments, the magnet 402 is a simple magnet without a core,such core described above in conjunction with FIG. 1. In otherembodiments, the magnet 402 has a core the same as or similar to thecore 20 described above in conjunction with FIG. 1. In still otherembodiments, the magnet 402 can have a core comprised of air or a corecomprised of a non-ferromagnetic material. The core can be aligned withan axis along or parallel the line 324.

Referring now to FIG. 5, an example of an electronic circuit 500 can bethe same as or similar to the electronic circuit 314 of FIGS. 3 and 4and can be coupled to magnetic field sensing elements 502, 508 the sameas or similar to the magnetic field sensing elements 304, 306 of FIGS. 3and 4. The electronic circuit 500 can include a first magnetoresistanceelement 502 coupled in a first half bridge with a fixed resistor 506.The electronic circuit 500 can also include a second magnetic resistanceelement 508 coupled in the second half bridge with a fixed resistor 504.The two half bridges can be driven from a voltage source 506, forming afull bridge circuit.

The first half bridge generates a signal 510 responsive to an externalmagnetic field. The second half bridge generates a signal 512 responsiveto the external magnetic field.

A differential amplifier 512 can be coupled to receive the signals 510,512 and configured to generate an amplified signal 512 a. It will beunderstood that the amplified signal 512 a is representative of adifference of signals generated by the two magnetoresistance elements502, 508.

An automatic gain control 514 can be coupled to receive the amplifiedsignal 512 a and configured to generate a gain controlled signal 514 a.A precision rotation detector 516 can be coupled to receive the gaincontrolled signal 514 a and configured to generate a precision patientdetector output signal 516 a. In some embodiments the precision rotationdetector output signal 516 a is a two state signal having high statesrepresentative, for example, of the proximity of teeth of theferromagnetic gear, which can be the same as or similar to theferromagnetic gear of FIGS. 3 and 4.

An output module 518 can be coupled to receive the precision rotationdetector output signal 516 a and configured to generate a signal 518 arepresentative of the precision rotation detector output signal 516 awith formats suitable for the application, for example, for anautomotive application.

In some embodiments, the electronic circuit 500 can also include amemory device 520, for example, an EEPROM or nonvolatile memory device,to receive and store automatic gain control values 514 a and thereafterto provide automatic gain control values 520 a to control the gain ofthe automatic gain control 514. With this arrangement, the electroniccircuit 500 can retain automatic gain control values, for example,during power down, and the stored automatic gain control values 520 acan be used upon power up to result in achieving a proper gain fasterafter power up. A similar memory device with stored automatic gaincontrol values can be used in any of the electronic circuits describedbelow.

While the EEPROM 520 is described above to retain automatic gain controlvalues, in other embodiments, the EEPROM 520 can retain other values,for example, threshold values, described below in conjunction with FIG.9, or other values also indicative of measured operationalcharacteristics of the magnetic field sensor.

Blocks of FIG. 5 can be implemented in analog circuits, digitalcircuits, or processors.

It will be recognized that, if the two magnetoresistance elements 502,508 experience the same magnetic field, then the amplified signal 512 ais not zero. Only when an edge of a gear tooth is proximate to themagnetoresistance elements 502, 508 will the amplified signal 512 a notbe zero. Thus, the electronic circuit 500 operates as an edge detector.Accordingly, the electronic circuit 500 does not include a true power onstate channel comparable to that described above in conjunction withFIG. 1A.

However, in an alternate arrangement, the magnetoresistance element 506and the resistor 502 can be interchanged in a similar electronic circuitor the magnetoresistance element 508 and the resistor 504 can beinterchanged in another similar circuit to achieve a tooth detector(i.e., feature detector). The similar circuits can include a true poweron state channel comparable to that described above in conjunction withFIG. 1A.

While two magnetoresistance elements 502, 508 are shown, in otherembodiments, the magnetoresistance elements 502, 508, and the bridgecircuit in which they are coupled, can be replaced with two Hall effectelements, for example, two vertical Hall effect elements.

Referring now to FIG. 6, a magnetic field sensor 600 is responsive to agear 622 having gear teeth, e.g., gear teeth 622 a, 622 b, 622 c. Themagnetic field sensor 600 can include a plurality of, i.e., two or more(or more than two), magnetic field sensing elements, e.g., 604 a,coupled to an electronic circuit 614. In some embodiments, the magneticfield sensing elements, e.g., 604 a, are separated in a direction alongan axis 606 between the plurality of magnetic field sensing elements,e.g., 604 a, by a distance between about 0.05 millimeters and about 2.0millimeters.

The plurality of magnetic field sensing elements, e.g., 604 a, and theelectronic circuit 614 can be disposed upon a major surface 602 a of(i.e., integrated within or upon) a substrate 602. For clarity, here themagnetic field sensing elements, e.g., 604 a, are shown to bemagnetoresistance elements. In other embodiments, the magnetic fieldsensing elements, e.g., 604 a, are Hall effect elements, e.g., verticalHall effect elements.

The magnetic field sensor 600 can also include a magnet 610. The magnet610 is configured to generate a magnetic field, which is generallydirected along an axis 608 at the position of the plurality of magneticfield sensing elements, e.g., 604 a, and is generally parallel to themajor surface 602 a of the substrate 602.

The plurality of magnetic field sensing elements, e.g., 604 a, haverespective maximum response axes parallel to the major surface 602 ofthe substrate 602. In some embodiments, the maximum response axes areparallel to each other. In some embodiments, the maximum response axesare substantially parallel to the axis 606. In other embodiments, themaximum response axes are substantially perpendicular to the axis 606.

A line perpendicular to the major surface 602 a of the substrate (i.e.,into the page) intersects the magnet 610 and does not intersect the gear622. Furthermore, the plurality of magnetic field sensing elements,e.g., 604 a, is disposed at a position such that the axis (e.g., 606)between (i.e., passing through) the plurality of magnetic field sensingelements, e.g., 604 a, does not intersect the gear 622. In someembodiments, the axis (e.g., 606) between (i.e., passing through) theplurality of magnetic field sensing elements, e.g., 604 a, issubstantially parallel to a tangent 630 to a direction of movement,e.g., 626, of the gear 622.

In the embodiment shown, a line between north (N) and south (S) poles ofthe magnet 610 is substantially parallel to the major surface 602 a ofthe substrate 602, and is substantially parallel to the axis (e.g., 606)between (i.e., passing through) the plurality of magnetic field sensingelements, e.g., 604 a. In some embodiments, the line between north andsouth poles does not intersect the ferromagnetic target object 622.

The electronic circuit 614 is configured to generate an output signal(not shown). An example of an electronic circuit is described more fullybelow in conjunction with FIGS. 8 and 9. Let is suffice here to say thatthe electronic circuit 614 is configured to compare each one of theplurality of magnetic field signals to a threshold signal to generate aplurality of binary signals. A plurality of states of the plurality ofbinary signals is indicative of a position of the ferromagnetic targetobject 622, and, in particular, a position of an edge of a gear tooth oran edge of a gear valley, relative to the plurality of magnetic fieldsensing elements. Thus, it will be apparent that the magnetic fieldsensor 600 can operate as an edge detector, a tooth detector, or both.

The output signal, when the gear 622 is rotating, is indicative speed ofrotation of the gear 622 and also indicative of positions of edges ofthe gear teeth. The magnetic field sensor 600 is able to provide a TPOSfunction, and, when the gear 622 is stationary, is able to identifywhether individual ones of the plurality of magnetic field sensingelements, e.g., 604 a, are proximate to a gear tooth or a valley in thegear 622.

Furthermore, the magnetic field sensor 600 is able to identify adirection of rotation of the gear 622 by way of a detected progressionof magnetic fields sensed by the plurality of magnetic field sensingelements, e.g., 604 a.

The magnet 610 can be comprised of one uniform material, and can have nocentral core, which is shown and described in conjunction with FIG. 1.However, in other embodiments, the magnet 610 can have a central corethe same as or similar to that shown and described in conjunction withFIG. 1. In still other embodiments, the magnet 610 can have a corecomprised of air or a core comprised of a non-ferromagnetic material.The core can be aligned parallel to the axis 606.

The magnetic field sensor 600 uses the plurality of magnetic fieldsensing elements, e.g., 604 a, to generate a respective plurality ofmagnetic field signals.

Each respective one of the plurality of magnetic field signals isresponsive to a magnetic field generated by the magnet 602 andinfluenced by a position of a ferromagnetic target object, e.g., gearteeth 622 a, 622 b, 622 c, relative to a position of each respective oneof the plurality of magnetic field sensing elements. The ferromagnetictarget object 622 is configured to move in a direction 626 of movement.The plurality of magnetic field sensing elements, e.g., 604 a, isdisposed along the axis 606, which is substantially parallel to thetangent 630.

In some alternate embodiments, the plurality of magnetic field sensingelements, e.g., 604 as, is disposed along an arc rather than along theline 606. A diameter of the arc can be the same as or similar to adiameter of the gear 622. The arc can be curved in the same direction asthe circumference of the gear, or in the other direction. When disposedin an arc, maximum response axes of the magnetic field sensing elementscan be parallel to each other, or thy may not be parallel to each other.This arrangement is shown below in conjunction with FIG. 16.

In some embodiments, the plurality of magnetic field sensing elements,e.g., 604 a, has a respective plurality of maximum response axesparallel to each other. In some embodiments, the maximum response axesare substantially parallel to the axis 606. In other embodiments, themaximum response axes are substantially perpendicular to the axis 606.

The magnetic field sensor 600 can be rotated in a direction 616 to anext position one hundred eighty degrees apart from the position shown,with no degradation of performance. However, intermediate rotations mayresult in a degradation of performance.

The magnetic field sensor 600 can be rotated in a direction of and arrow618 with a center of rotation anywhere along a line 624, throughapproximately +/−twenty degrees, without substantial degradation ofperformance.

In some embodiments, the magnetic field sensing elements, e.g., 604 a,are magnetoresistance elements. In other embodiments, the magnetic fieldsensing elements are Hall effect elements, e.g., vertical Hall effectelements. However, it is advantageous to use magnetic field sensingelements for which respective axes of maximum sensitivity are parallelto the axis 606.

Referring now to FIG. 7, in which like elements of FIG. 6 are shownhaving like reference designations, a magnetic field sensor 700 is likethe magnetic field sensor 600 of FIG. 6. However, the magnetic fieldsensor 700 has a different magnet 702 for which a line between north (N)and south (S) poles of the magnet 702 is substantially parallel to themajor surface 602 a of the substrate 602, and substantiallyperpendicular to the axis (e.g., 606) between (i.e., passing through)the plurality of magnetic field sensing elements, e.g., 604 a. In someembodiments, the line between the north and south poles of the magnet702 is in a direction toward the gear 622 and intersects the gear 622.

Referring now to FIG. 8, an electronic circuit 800 can be the same as orsimilar to electronic circuit 614 of FIGS. 6 and 7 and coupled to aplurality of magnetoresistance elements, which can be the same as orsimilar to the plurality of magnetic field sensing elements, e.g., 604a, of FIGS. 6 and 7.

The electronic circuit 800 can include a plurality of electronicchannels, of which a channel having a magnetoresistance element 802 anda fixed resistor 804 is but one example. The plurality of electronicchannels can be coupled to receive a voltage from a voltage regulator806. Taking the magnetoresistance element 802 and the fixed resistor804, which form a voltage divider, as being representative of elementsof other ones of the electronic channels, a voltage signal 808 can begenerated at the junction between the magnetoresistance element 802 anda fixed resistor 804. The voltage signal 808 has a value representativeof a magnitude of the magnetic field experienced by themagnetoresistance element 802. Other ones of the electronic channelsgenerate voltage signals having values representative of magnetic fieldsexperienced by other ones of the magnetoresistance elements.

In some embodiments, a quantity of the magnetoresistance elements can bein the range of two to nine.

In other embodiments, the voltage source can be replaced with a currentsource or with separate current sources to drive each resistor divider,e.g., 802, 804. In some embodiments, the separate current sources can beseparate controlled legs of current mirrors, each having the samereference leg.

The voltage signal 808 is received by an amplifier 810 The amplifier 810configured to generate an amplified voltage signal 810 a. A comparator812 is coupled to receive the amplified voltage signal 810 a, coupled toreceive a threshold signal 818, and configured to generate a comparisonsignal 812 a (i.e., a binary, two-state, signal).

In some other embodiments, the amplifiers, e.g., 810, are not used.

A nonvolatile memory device, for example, an electrically erasable readonly memory (EEPROM) 814, is coupled to receive a plurality of suchcomparison signals at a multi-bit address input. The EEPROM 814 producesan output signal 814 a, which can be a single bit output signal or amulti-bit output signal. The output signal 814 a can have a value, i.e.,a digital value, representative of a position of a gear tooth relativeto the plurality of magnetoresistance elements, for example, a positionof the gear tooth 322 b of FIG. 6 relative to a position of theplurality of magnetic field sensing elements shown in FIG. 6. Thus, oneor more states of the signal 814 a are representative of an edge of thegear tooth 622 b being proximate to the plurality of magnetic fieldsensing elements.

It will be appreciated that the EEPROM 814 can act as a look-up table,and can provide any desired mapping of address to output signal 814 a.The same electronic circuit can be applied to both the magnetic fieldsensor 600 of FIG. 6 and to the magnetic field sensor 700 of FIG. 7, butperhaps with different look up tables stored in the EEPROM 814.

The signal 814 a can be indicative of a speed of rotation and/or adirection of rotation of the ferromagnetic target object, e.g., 622 ofFIG. 6.

In some other embodiments, the EEPROM 814 is replaced by a processor.

In some embodiments, the output signal 814 a is received by an outputprotocol module 816. The output protocol module 816 is configured togenerate a formatted signal 816 a in a selected one of a plurality offormats including, but not limited to, a SENT format, an I2C format, aPWM format, or a binary format.

The formatted signal 816 a can also be indicative of a speed of rotationand/or a direction of rotation of the ferromagnetic target object, e.g.,622 of FIG. 6. To this end, the output protocol module 816 can use thesignal 814 a to identify the speed of rotation and/or the direction ofrotation of the ferromagnetic target object. Certain digital values ofthe signal 814 a may be indicative of a center of a ferromagnetic targetfeature (e.g., gear tooth) being proximate to the plurality ofmagnetoresistance elements, certain other digital values of the signal814 a may be indicative of a particular edge of a ferromagnetic targetobject feature being proximate to the plurality of magnetoresistanceelements, and certain other digital values of the signal 814 a may beindicative of a different particular edge of a ferromagnetic targetobject feature being proximate to the plurality of magnetoresistanceelements.

While the electronic circuit 800 is shown to have a plurality of simplevoltage dividers, e.g., a voltage divider formed from themagnetoresistance element 802 with the fixed resistor 804, in otherembodiments, each channel can use a different arrangement, for example,a Wheatstone (full) bridge.

In still other embodiments, each one of the electronic channels can usea respective Hall effect element, e.g., a respective vertical Halleffect element. As is known, a Hall element can receive, i.e., can bedriven by, either a voltage source or a current source, and the Halleffect element can generate, from two output signal nodes, adifferential output signal. It should be apparent how the electroniccircuit 800 can be modified to use Hall effect elements instead ofmagnetoresistance elements.

While a plurality of comparators (e.g., 812) is shown, in otherembodiments, there can be one or more comparators that are multiplexedto provide parallel channels. Similarly, while a plurality of amplifiers810 is shown, in other embodiments, one or more amplifiers can bemultiplexed to provide the parallel channels.

Referring now to FIG. 9, in which like elements of FIG. 8 are shownhaving like reference designations, an electronic circuit 900 can be thesame as or similar to electronic circuit 614 of FIGS. 6 and 7, andcoupled to a plurality of magnetoresistance elements, which can be thesame as or similar to the plurality of magnetic field sensing elements,e.g., 604 a, of FIGS. 6 and 7.

The electronic circuit 900 can include a plurality of electronicchannels, of which a channel having the magnetoresistance element 802and a fixed resistor 804 is but one example. Taking this channel asbeing representative of other ones of a plurality of channels, ananalog-to-digital converter (ADC) 912 can be coupled to receive theamplified voltage signal 810 a and configure to generate a convertedsignal 902 a.

A position calculation module 904 (i.e., a processor) can be coupled toreceive the converted signal 902 a. In particular, a digital comparator906 within the position calculation module 904 can be coupled to receivethe converted signal 902 a. The digital comparator 906 can also becoupled to receive a digital threshold value 905 and configured togenerate a comparison signal 906 a.

In some embodiments, a nonvolatile memory device, for example, an EEPROM908, can be coupled to receive the comparison signal 906 a along withother comparison signals. The EEPROM 908 can include a lookup table 909to receive the comparison signals and to generate a signal 908 a, whichcan be a single bit signal or a multi-bit signal. The signal 908 a canbe the same as or similar to the signal 814 a of FIG. 8.

The signal 908 a can be indicative of a speed of rotation and/or adirection of rotation of the ferromagnetic target object, e.g., 622 ofFIG. 6.

An output protocol module 910 can receive the signal 908 a and cangenerate a formatted signal 910 a, which can be the same as or similarto the formatted signal 816 a of FIG. 8.

The formatted signal 910 a can be indicative of a speed of rotationand/or a direction of rotation of the ferromagnetic target object, e.g.,622 of FIG. 6. To this end, the output protocol module 910 can use thesignal 908 a to identify the speed of rotation and/or the direction ofrotation of the ferromagnetic target object. Certain digital values ofthe signal 908 a may be indicative of a center of a ferromagnetic targetfeature (e.g., gear tooth) being proximate to the plurality ofmagnetoresistance elements, certain other digital values of the signal908 a may be indicative of a particular edge of a ferromagnetic targetobject feature being proximate to the plurality of magnetoresistanceelements, and certain other digital values of the signal 908 a may beindicative of a different particular edge of a ferromagnetic targetobject feature being proximate to the plurality of magnetoresistanceelements.

In some embodiments, the position calculation module 904 can alsoinclude a threshold calculation module 912 coupled to receive one ormore of the converted signals 903.

In operation, the threshold calculation module 912 can identify desiredthreshold values, e.g., 905, to use as inputs to the digitalcomparators, e.g., 906. For example, in some embodiments, the thresholdcalculation module 912 can calculate positive and negative peak valuesof the converted signals 903, can compute peak-to-peak values, and cancompute respective threshold values to be desired percentages of thepeak-to peak values. For example, in some embodiments, calculatedthresholds can be approximately 60 percent and approximately fortypercent of the peak-to-peak values. Accordingly, the positioncalculation 10 module 904 can store in a threshold storage region 911 ofthe EEPROM 906, the calculated threshold values, and can supply thecalculated threshold values from the threshold storage area 911 to thedigital comparators, e.g., 906.

With the above arrangement, after a power down to the electronic circuit900, upon powering up again, the stored threshold values can be rapidlyused, resulting in a faster power up response time.

While separate analog-to-digital converters are shown on each channel,in other embodiments, there can be one or more analog-to digitalconverters coupled to the amplifiers, e.g., 810, through a multiplexer(not shown). Similarly, while a plurality of comparators is shown, inother embodiments, there can be one or more comparators coupled to theone or more analog-to-digital converters and coupled to the processor908 through a multiplexer (not shown.

While the EEPROM 908 is shown to be within the position calculationmodule 904, in other embodiments, the EEPROM 908 is outside of theposition calculation module 904.

Some other embodiments are a combination of parts of FIGS. 8 and 9. Forexample, in some other embodiments, the analog-to-digital converters,e.g., 902, are not used, in which case, the plurality of comparators,e.g., 906 can be, for example, analog comparators that provide thecomparison signals, e.g., 906, as binary signals to the positioncalculation module 904. Accordingly, the EEPROM 908 (or the thresholdcalculation module 912), through one or more digital-to-analogconverters (DACs, not shown), can provide analog threshold signals tothe comparators.

In still other embodiments, the threshold calculation module 912 can bean analog module operable to identify positive and negative peaks of theamplified signals, e.g., 810 a, operable to provide associatedthresholds between the positive and negative peaks, and operable toprovide the thresholds to the comparators, e.g., 906, as analogthresholds. This arrangement can be the same as or similar to parts ofthe precision rotation detectors described above in conjunction withFIG. 1A, for which reference is made above to prior art patents andpatent applications.

Referring now to FIG. 10, a magnetic field sensor 1000 is responsive toa gear 1022 having gear teeth, e.g., gear teeth 1022 a, 1022 b, 1022 c.The magnetic field sensor 1000 can include a CVH sensing element 1004having a plurality of vertical Hall effect elements coupled to anelectronic circuit 1014. In some embodiments, a diameter of the CVHsensing element 1004 is between about 0.1 millimeters and about 1.0millimeters.

The CVH sensing element 1004 and the electronic circuit 1014 can bedisposed upon a major surface 1002 a of (i.e., integrated within orupon) a substrate 1002.

The magnetic field sensor 1000 can also include a magnet 1010. Themagnet 1010 is configured to generate a magnetic field, which isgenerally directed along an axis 1024 at the position of the CVH sensingelement 1004 and is generally parallel to the major surface 1002 a ofthe substrate 1002.

The vertical Hall effect sensing elements within the CVH sensing element1004 have respective maximum response axes parallel to the major surface1002 of the substrate 1002.

A line perpendicular to the major surface 1002 a of the substrate (i.e.,into the page) intersects the magnet 1010 and does not intersect thegear 1022.

In the embodiment shown, a line between north (N) and south (S) poles ofthe magnet 1010 is substantially parallel to the major surface 1002 a ofthe substrate 1002. In some embodiments, the line between the north andsouth poles of the magnet 1010 intersects the gear 1022 and is in adirection toward the gear 1022. In some other embodiments, the linebetween the north and south poles of the magnet 1010 is substantiallyparallel to the line 1006 and does not intersect the gear 1022.

The electronic circuit 1014 is configured to generate an output signal(not shown). Let it suffice here to say that the electronic circuit 1014is configured to generate an x-z angle signal having x-z angle valuesrepresentative of an angle (i.e., direction) of a magnetic fieldexperienced by the CVH sensing element 1004. Thus, it will be apparentthat the magnetic field sensor 1000 can operate as an edge detector oras a tooth detector.

The output signal, when the gear 1022 is rotating, is indicative of aspeed of rotation of the gear 1022 and also indicative of positions ofedges of the gear teeth and also positions of the gear teeth. Themagnetic field sensor 1000 is able to provide a TPOS function, and, whenthe gear 1022 is stationary, is able to identify whether the CVH sensingelement 1004 is proximate to a gear tooth or a valley in the gear 1022.

The magnet 1010 can be comprised of one uniform material, and can haveno central core, which is shown and described in conjunction withFIG. 1. However, in other embodiments, the magnet 1010 can have acentral core the same as or similar to that shown and described inconjunction with FIG. 1. In still other embodiments, the magnet 1010 canhave a core comprised of air or a core comprised of a non-ferromagneticmaterial. In some embodiments, the central core can have an axissubstantially parallel to an axis 1024.

The magnetic field sensor 1000 uses the CVH sensing element 1004 togenerate one sequential magnetic field signal.

The sequential magnetic field signal is responsive to a magnetic fieldgenerated by the magnet 1010 and influenced by a position of aferromagnetic target object, e.g., gear teeth 1022 a, 1022 b, 1022 c,relative to a position of each respective one of the plurality ofmagnetic field sensing elements. The ferromagnetic target object 1022 isconfigured to move in a direction 1026 of movement. A tangent 1030 tothe direction of movement 1026 is shown.

The magnetic field sensor 1000 can be rotated in a direction 1016 to anext position one hundred eighty degrees apart from the position shown,with no degradation of performance. However, intermediate rotations mayresult in a degradation of performance.

The magnetic field sensor 1000 can be rotated in a direction of andarrow 1018 with a center of rotation anywhere along a line 1024, throughapproximately +/−twenty degrees, without substantial degradation ofperformance.

In some alternate embodiments, the CVH sensing element 1004 is replacedby a plurality of separately isolated vertical Hall effect elements.

In some alternate arrangements, there can be two or more CVH sensingelements disposed upon the substrate, substantially along the axis 1006.

Full operation of the CVH sensing element 1004 and the electroniccircuit 1014 of FIG. 10 is described in more detail in PCT PatentApplication No. PCT/EP2008/056517, entitled “Magnetic Field Sensor forMeasuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008,which is published in the English language as PCT Publication No. WO2008/145610.

Referring now to FIG. 11, the two magnetic field sensing elements ofFIGS. 3, 4, and 5, shown to be two magnetoresistance elements coupled ina bridge arrangement in FIG. 5, can instead be separatelymagnetoresistance elements coupled to respective current sources. Itshould be apparent how the two magnetoresistance elements of FIG. 15 canbe coupled to the electronic circuit of FIG. 5. It should be noted thata signal, −V2, is inverted relative to a signal, V2, shown in FIG. 5,and thus must be inverted to couple as the signal, V2, in FIG. 5 toachieve the same functionality described as an edge detector in FIG. 5.

Referring now to FIG. 12, a magnetic field sensor 1200 can be the sameas or similar to the magnetic field sensor 300 of FIG. 3, the magneticfield sensor 600 of FIG. 6, or the magnetic field sensor 1000 of FIG. 10(but with the magnet rotated ninety degrees). A block 1204 isrepresentative of the magnetic field sensing elements 304, 306 of FIG.3, the plurality of magnetic field sensing elements, e.g., 604 a, ofFIG. 6, or the CVH sensing element 1004 of FIG. 10. A block 1214 isrepresentative of the electronic circuit 314 of FIG. 3, the electroniccircuit 614 of FIG. 6, or the electronic circuit 1014 of FIG. 10.

The block 1204 representative of magnetic field sensing elements isdisposed on a surface 1202 a of a substrate 1202. The magnetic fieldsensor 1200 can include a magnet 1232 disposed as shown behind thesubstrate 1202 such that a line perpendicular to the substrate 1202intersects the magnet 1232. North and south poles of the magnet 1232 canbe arranged as shown to be like the alignment of magnets 332, 610 FIGS.3 and 6, respectively, or like the magnet 1010 of FIG. 10, but rotatedninety degrees.

Unlike the magnetic field sensors shown above, here the substrate 1202and the block 1204 representative of magnetic field sensing elementsoverlap a ferromagnetic target object 1222. The ferromagnetic targetobject 1222 is shown here to be a ferromagnetic gear having gear teeth,e.g., 1222 a, 1222 b, 1222 c. In another embodiment the magnet 1232 andferromagnetic target object 1222 can be replaced by a ring magnet orpermanent magnet (hard ferromagnetic material) as described below inconjunction with FIGS. 14 and 15.

The magnetic field sensor 1200 can be rotated in a direction 1212 to anext position one hundred eighty degrees apart from the position shown,with no degradation of performance. However, intermediate rotations mayresult in a degradation of performance or may not be possible due tocontact with the ferromagnetic target object 1222.

The magnetic field sensor 1200 can be rotated in a direction of andarrow 1216 with a center of rotation anywhere along a line 1224, throughapproximately +/−twenty degrees, without substantial degradation ofperformance.

Referring now to FIG. 13, in which like elements of FIG. 12 are shownhaving like reference designations, a magnetic field sensor 1300 is likethe magnetic field sensor 1200 of FIG. 12. However, unlike the magneticfield sensor 1200 of FIG. 12, the magnetic field sensor 1300 includes amagnet 1302 having north and south poles arranged as shown,perpendicular to the north and south pole arrangement of the magnet 1232of FIG. 12.

All magnetic field sensors shown and described above are shown to sensea movement of ferromagnetic target object in the form of a gear or cam.However, FIGS. 14 and 15 described below show the same or similarmagnetic field sensors for sensing movement of a ring magnet. Commentsmade above about edge detectors, tooth detectors, and TPOS functionsapply in the same way when sensing a ring magnet.

Referring now to FIG. 14, in which like elements of FIG. 12 are shownhaving like reference designations, a magnetic field sensor 1400 is likethe magnetic field sensors described above. However, the magnetic fieldsensor 1400 has no internal magnet. Instead, the magnetic field sensor1400 is responsive to passing magnetic domains of a ring magnet 1402. Nand S designations shown can be indicative of north and south polesassociated with the ring magnet target. A S or N pole would exist on theother side of the page if magnetized perpendicular to the page. In otherembodiments the N and S would be on the outer radial dimension towardthe ring magnet while a complimentary S or N would exist on the innerradial side of the ring magnet.

In some embodiments, the magnetic domains of the ring magnet 1402 aremagnetized parallel to the page. In some other embodiments, the magneticdomains of the ring magnet 1402 are magnetized perpendicular to thepage.

Referring now to FIG. 15, in which like elements of FIG. 14 are shownhaving like reference designations, a magnetic field sensor 1500 is likethe magnetic field sensors described above. However, the magnetic fieldsensor 1500 has no internal magnet. Instead, the magnetic field sensor1500 is responsive to passing magnetic domains of the ring magnet 1402.

Unlike the magnetic field sensor 1400 of FIG. 14, the substrate 1202overlaps the ring magnet 1402 such that a line perpendicular to thesubstrate 1202 intersects the ring magnet 1402. In other embodiments,more of the substrate 1202, or the entire substrate 1202, overlaps thering magnet 1402.

Referring now to FIG. 16, a plurality of magnetic field sensingelements, e.g., 1602 a, can be used as the plurality of magnetic fieldsensing elements, e.g., 604 a, of the magnetic field sensors 600, 700 ofFIGS. 6 and 7. However, unlike the plurality of magnetic field sensingelements, e.g., 604 a, of the magnetic field sensors 600, 700 of FIGS. 6and 7, the magnetic field sensing elements, e.g., 1602 a, can bedisposed in an arc 1600. In some embodiments, a radius of curvature ofthe arc 1600 can be the same as a radius of curvature of a ring magnet1604 (or alternatively, a gear) to which the magnetic field sensingelements, e.g., 1602 a, are responsive. However, other radii ofcurvatures are also possible.

In some alternate arrangements represented, for example, by the magneticfield sensor 1500 of FIG. 15, the magnetic field sensing elements, e.g.,1602 a, can be disposed over and overlap the ring magnet 1604.

In some embodiments, maximum response axes of the plurality of magneticfield sensing elements, e.g., 1602 a, are parallel to each other.

In some embodiments, maximum response axes of the plurality of magneticfield sensing elements, e.g., 1602 a, are not parallel to each other.

In some other embodiments, the plurality of magnetic field sensingelements is arranged in a straight line, which is not parallel to atangent to the ring magnet 1604, i.e., which is at a diagonal to thering magnet 1604.

While ferromagnetic target objects in the form of ferromagnetic gearsand ferromagnetic ring magnets are described above, in otherembodiments, any of the ferromagnetic target objects can be replaced bya non-ferromagnetic target object. In these embodiments, thenon-ferromagnetic target object can be an electrically conductive targetobject in which eddy currents can be generated by rotation of thenon-ferromagnetic conductive target object in the presence of a magneticfield, which may be supplied by a magnet the same as or similar to themagnets 332, 610 of FIGS. 3 and 6, respectively, or the same as orsimilar to the magnet 1010 of FIG. 10. In other embodiments, a coil oran electromagnet may provide the magnetic field. The above-describedmagnetic field sensing elements can be responsive to magnetic fieldsgenerated by the eddy currents in the non-ferromagnetic conductivetarget objects. Arrangements responsive to eddy currents are described,for example, in U.S. patent application Ser. No. 13/946,417, filed Jul.19, 2013, and entitled “Methods And Apparatus For Magnetic Sensor HavingAn Integrated Coil Or Magnet To Detect A Non-Ferromagnetic Target,”which supplication is assigned to the assignee of the presentapplication, and which application is incorporated by reference hereinin its entirety.

From the above, it will be understood that the target object sensed withmagnetic field sensors described herein can be a ferromagnetic targetobject (e.g., a gear of a ring magnet) or a non-ferromagnetic conductiveobject (e.g., a gear).

Magnetic field sensors described above use a sensed position of thesensed object to identify speed and/or direction of rotation.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that the scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

What is claimed is:
 1. A magnetic field sensor for measuring movement ofa target object, the movement in an x-z plane within x-y-z Cartesiancoordinates with x, y, and z orthogonal axes, the magnetic field sensorcomprising: a substrate having a major planar surface within abouttwenty degrees of parallel to the x-z plane; and an electronic circuitdisposed upon the substrate, the electronic circuit comprising: aplurality of magnetic field sensing elements disposed upon the majorplanar surface of the substrate, the plurality of magnetic field sensingelements including two magnetic field sensing elements disposed upon themajor planar surface of the substrate, the two magnetic field sensingelements having respective major response axes parallel to the majorplanar surface of the substrate, the two magnetic field sensing elementshaving the respective major response axes parallel to each other, a linepassing through any two of the plurality of magnetic field sensingelements not intersecting the target object, wherein the two magneticfield sensing elements are configured to generate a respective twomagnetic field signals; and a differential amplifier coupled to receivethe two magnetic field signals and configured to generate an outputsignal as a difference of the two magnetic field signals, the outputsignal indicative of a position of the target object relative to the twomagnetic field sensing elements, wherein the major planar surface of thesubstrate overlaps the target object such that a line perpendicular tothe major planar surface of the substrate, within twenty degrees ofparallel to an axis of rotation of the target object, and passingthrough at least one of the two magnetic field sensing elementsintersects the target object, and a line parallel to the major planarsurface of the substrate is in a direction toward the target object. 2.The magnetic field sensor of claim 1, further comprising: a magnetfixedly coupled to the substrate, the magnet having at least two polesto generate a magnetic field parallel to the major planar surface of thesubstrate.
 3. The magnetic field sensor of claim 1, wherein the targetobject comprises a ring magnet having a plurality of alternating northand south poles, the target object to generate a magnetic field parallelto the major planar surface of the substrate.
 4. The magnetic fieldsensor of claim 1, wherein the two magnetic field sensing elementscomprise planar Hall elements.
 5. The magnetic field sensor of claim 1,wherein the two magnetic field sensing elements comprise vertical Hallelements.
 6. The magnetic field sensor of claim 1, wherein the twomagnetic field sensing elements comprise magnetoresistance elements. 7.A magnetic field sensor for measuring movement of a target object, themovement in an x-z plane within x-y-z Cartesian coordinates with x, y,and z orthogonal axes, the magnetic field sensor comprising: means forreceiving, within the magnetic field sensor, two magnetic field signalsgenerated by a plurality of magnetic field sensing elements disposedupon the major planar surface of the substrate, the plurality ofmagnetic field sensing elements including two magnetic field sensingelements, the two magnetic field sensing elements disposed upon asubstrate, the substrate having a major planar surface within abouttwenty degrees of parallel to the x-z plane, the two magnetic fieldsensing elements having respective major response axes parallel to themajor planar surface of the substrate, the two magnetic field sensingelements having the respective major response axes parallel to eachother, a line passing through any two of the plurality of magnetic fieldsensing elements not intersecting the target object; and means forgenerating, within the magnetic field sensor, an output signal as adifference of the two magnetic field signals, the output signalindicative of a position of a target object relative to the two magneticfield sensing elements, wherein the major planar surface of thesubstrate overlaps the target object such that a line perpendicular tothe major planar surface of the substrate, within twenty degrees ofparallel to an axis of rotation of the target object, and passingthrough at least one of the two magnetic field sensing elementsintersects the target object, and a line parallel to the major planarsurface of the substrate is in a direction toward the target object. 8.The magnetic field sensor of claim 7, further comprising: means forgenerating a magnetic field parallel to the major planar surface of thesubstrate.
 9. The magnetic field sensor of claim 7, wherein the targetobject comprises a ring magnet having a plurality of alternating northand south poles, the target object to generate a magnetic field parallelto the major planar surface of the substrate.
 10. The magnetic fieldsensor of claim 7, wherein the two magnetic field sensing elementscomprise planar Hall elements.
 11. The magnetic field sensor of claim 7,wherein the two magnetic field sensing elements comprise vertical Hallelements.
 12. The magnetic field sensor of claim 7, wherein the twomagnetic field sensing elements comprise magnetoresistance elements. 13.A magnetic field sensor for measuring movement of a target object, themovement parallel to an x-z plane within x-y-z Cartesian coordinateswith x, y, and z orthogonal axes, the magnetic field sensor comprising:a substrate having a major planar surface within about twenty degrees ofparallel to the x-z plane; a plurality of magnetic field sensingelements disposed upon the major planar surface of the substrate, eachone of the plurality of magnetic field sensing elements having a majorresponse axis substantially parallel to the major planar surface of thesubstrate, and the plurality of magnetic field sensing elements isconfigured to generate a respective plurality of magnetic field signals,wherein the plurality of magnetic field sensing elements is formed as atleast one circular vertical Hall (CVH) sensing element; and a magnetfixedly coupled to the substrate, the magnet having at least two polesto generate a magnetic field substantially parallel to the major planarsurface of the substrate.
 14. The magnetic field sensor of claim 13,further comprising: an electronic circuit disposed upon the substrateand coupled to the plurality of magnetic field sensing elements, theelectronic circuit comprising: a non-volatile memory device operable tostore a value indicative of a measured operational characteristic of themagnetic field sensor.
 15. The magnetic field sensor of claim 14,wherein the stored value is stored during a first time period, andwherein the stored value is recalled and used during a second differenttime period after the first time period.
 16. The magnetic field sensorof claim 13, further comprising: an electronic circuit disposed upon thesubstrate and coupled to the plurality of magnetic field sensingelements, the electronic circuit comprising: an output protocol moduleoperable to use the plurality of magnetic field signals to determine adirection of movement of the target object.
 17. The magnetic fieldsensor of claim 13, wherein the major planar surface of the substrateoverlaps the target object such that a line perpendicular to the majorplanar surface of the substrate and passing through at least one of theplurality of magnetic field sensing elements intersects the targetobject, and a line parallel to the major planar surface of the substrateis in a direction of the target object.
 18. The magnetic field sensor ofclaim 13, wherein the target object comprises a ring magnet having aplurality of alternating north and south poles, the target object togenerate a magnetic field substantially parallel to the major planarsurface of the substrate.
 19. The magnetic field sensor of claim 18,wherein the major planar surface of the substrate overlaps the targetobject such that a line perpendicular to the major planar surface of thesubstrate and passing through at least one of the plurality of magneticfield sensing elements intersects the target object, and a line parallelto the major planar surface of the substrate is in a direction of thetarget object.
 20. The magnetic field sensor of claim 13, wherein theplurality of magnetic field sensing elements is arranged in a linewithin about twenty degrees of parallel to the x-axis.
 21. The magneticfield sensor of claim 2, wherein the two magnetic field sensing elementscomprise first and second magnetic field sensing elements, wherein afirst distance between a surface of the magnet and the target object issmaller than a second distance between the first magnetic field sensingelement and the target object.
 22. The magnetic field sensor of claim 2,wherein a line disposed upon the major planar surface of the substrateintersects the target object.
 23. The magnetic field sensor of claim 1,wherein the two magnetic field sensing elements have a separationbetween about one half and about one and one half of a width of afeature of the target object.
 24. The magnetic field sensor of claim 1,wherein the line passing through the two magnetic field sensing elementsis substantially parallel to a tangent to a direction of movement of thetarget object.
 25. The magnetic field sensor of claim 2, wherein a lineperpendicular to the major planar surface of the substrate intersectsthe magnet.
 26. The magnetic field sensor of claim 13, wherein a lineperpendicular to the major planar surface of the substrate intersectsthe magnet.
 27. The magnetic field sensor of claim 2, wherein a lineparallel to the major planar surface of the substrate intersects theaxis of rotation of the target object.
 28. The magnetic field sensor ofclaim 8, wherein a line disposed upon the major planar surface of thesubstrate intersects the target object.
 29. The magnetic field sensor ofclaim 8, wherein a line parallel to the major planar surface of thesubstrate intersects the axis of rotation of the target object.
 30. Themagnetic field sensor of claim 13, wherein a line disposed upon themajor planar surface of the substrate intersects the target object. 31.The magnetic field sensor of claim 13, wherein a line parallel to themajor planar surface of the substrate intersects the axis of rotation ofthe target object.